Download November - LVAstronomy.com

MONTHLY OBSERVER’S CHALLENGE
Las Vegas Astronomical Society
Compiled by:
Roger Ivester, Boiling Springs, North Carolina
&
Fred Rayworth, Las Vegas, Nevada
With special assistance from:
Rob Lambert, Las Vegas, Nevada
NOVEMBER 2015
Introduction
The purpose of the Observer’s Challenge is to encourage the pursuit of visual observing. It’s open to everyone
that’s interested, and if you’re able to contribute notes, and/or drawings, we’ll be happy to include them in our
monthly summary. We also accept digital imaging. Visual astronomy depends on what’s seen through the
eyepiece. Not only does it satisfy an innate curiosity, but it allows the visual observer to discover the beauty
and the wonderment of the night sky. Before photography, all observations depended on what the astronomer
saw in the eyepiece, and how they recorded their observations. This was done through notes and drawings, and
that’s the tradition we’re stressing in the Observers Challenge. We’re not excluding those with an interest in
astrophotography, either. Your images and notes are just as welcome. The hope is that you’ll read through
these reports and become inspired to take more time at the eyepiece, study each object, and look for those subtle
details that you might never have noticed before.
NGC-7789 – (CR-460) – Open Cluster In Cassiopeia
NGC-7789 is a medium-small open cluster in Cassiopeia. It’s also known as Collinder 460 as well as Melotte
245. However, it was discovered by Caroline Herschel in 1783 and they gave it the designation H-056-7. It’s
known as the White Rose Cluster or Caroline’s Rose. The name came from the impression some visual
observers get in smaller scopes by the star patterns which can resemble the swirls of a rose as seen from above
(Wikipedia).
The cluster lays approximately 7.6 lightyears away and shines at a respectable mag. 6.7. It stands out as a
distinct clump within a rich star field and presents a nice challenge for all apertures.
Observations/Drawings/Photos (Contributors listed in alphabetical order)
Glenn Chaple: Observer from
Massachusetts
I just got in from making an
observation of NGC-7789 on
December 3, 2015. The attached
sketch was based on an observation
made with a 4-inch f/4 rich field
telescope. Magnification was 28X
and the field diameter was 3°.
I saw a ghostly circular glow,
sprinkled with tiny stellar specks.
James Dire: Observer from Hawaii
The Constellation Cassiopeia resides along the bright swath of starry glow
known as the Milky Way. We know this glow is the plane of our home galaxy
and holds a multitude of open star clusters. Dozens of these galactic clusters are
found in Cassiopeia. One of the finest, but often overlooked, is NGC-7789.
Cassiopeia is one of the most recognized constellations. The constellation is
circumpolar for anyone north of a line from San Francisco to Baltimore. When
high above Polaris, five of its brightest stars roughly trace out the letter ‘M’.
These stars from left to right (west to east) are named Caph, Shedar, Navi,
Ruchbah, and Segin. NGC-7789 can be found 3° south-southwest of Caph.
Note that south is the direction away from Polaris and west is to the left of the
big M. In binoculars or a finder scope, you will see NGC-7789 about halfway
between the stars Sigma and Rho Cassiopeiae. Both stars are approximately
mag. 4.6. Sigma is a blue-white star and Rho is a yellow star.
NGC-7789 is worthy of being in Charles Messier’s catalog, but Messier never recorded it. The cluster was
discovered by Caroline Herschel in 1783. It is often called Caroline’s Rose because its loops of stars and dark
lanes trace out the pattern of rose petals, more clearly imagined at the eyepiece than in photographs.
Caroline’s Rose is a rich, dense star cluster that is
easily resolved. It is 25 arc minutes in diameter and
its integrated mag. is 6.7. The brightest members of
the cluster are mag. 11 and 12 stars and there are
more than 150 stars inside the inner 16-arc minute
diameter region. The cluster is 8,000 light-years away
and thought to be around 1.6 billion years old.
My image of NGC-7789 was taken with a 10-inch,
f/4 Newtonian with a coma corrector using a SBIG
ST-2000XCM CCD camera. The exposure was 30
minutes. North is up and east is to the left. The
image is 33 by 25 arc minutes, so most of the stars on
it are members of the cluster. The bright red star on
the right side of the cluster is SAO 35903, mag. 8.4.
Above and to the right of this lies the second brightest star in the image, a mag. 9.4 white star. The red star on
the upper left side of the image is mag. 9.8. All three of these stars are not members of the cluster but
foreground objects!
In a 6- to 8-inch telescope, the clusters stars appear very uniform in brightness. I viewed it with my 6-inch f/6
Newtonian with a 13mm eyepiece. The cluster filled most of the field of view and the rose petals were quite
obvious.
Roger Ivester: LVAS Member from North Carolina
I observed NGC-7789, the open cluster in Cassiopeia on October
7, 2015. The conditions were good with a NELM of 5.2. I used
a 10-inch f/4.5 Newtonian reflector with a magnification of
104X, (FOV: 0.79°), the same as applied to the sketch.
It was very bright and rich and I counted well over 120 stars.
The cluster stars encompassed an area of about 25 arcminutes. I
saw loops of stars with dark lanes throughout, but they mostly
appeared to be a random scattering. A brighter mag. 9 star was
located just off the cluster edge toward the west.
Gus Johnson: Observer from Maryland
I observed NGC-7789, the open cluster in Cassiopeia with a 10inch Newtonian reflector.
At higher power, I saw a bright splash of bright and dimmer
stars, taking up a full 1/4º and noted some dark lanes. At low
magnification, I saw a very large hazy patch, and resolved many
of the brighter stars.
Rob Lambert: LVAS President from Las Vegas
I observed NGC-7789 during the LVAS Fall Campout and Star
Party at Cathedral Gorge near Panaca, NV in September 2015.
Cathedral Gorge is a favorite observing venue of the LVAS and
we normally go there twice a year. Two great nights of
observing allowed me to capture these two images of the “White
Rose” Cluster.
I’m not sure that I can see or imagine the
rose in either of my images of the cluster.
The first image was captured with my
80mm Apochromatic Refractor and
Mallincam VSS+ camera. The exposure
was only 3 seconds and approximates what
one will see at the eyepiece when observing
this cluster. At this exposure, the image
reveals a hundred or more stars in the
central cluster. North is to the left and east
is down.
The field of view is
approximately 2° with a magnification of
30X. There is a chain of brighter stars that
crosses the western half of the cluster. The
brighter stars are mags. 10 and 11 while the
dimmer stars of the cluster are mag 12 or
dimmer. The brightest star in the image is
TYC4009-2201-1 shines at mag. 8.4.
The second image was captured with my
Explore Scientific ED 127 Apochromatic
Refractor.
The field of view is
approximately 0.8 degrees with a
magnification of 60x. The exposure was 10
seconds and it highlights the brighter stars
in the cluster while suppressing the dimmer
stars. In this image the snake-like chain of
bright stars crossing the cluster is more
visible.
Fred Rayworth: LVAS Vice President and AL Coordinator
from Nevada
The first time I observed NGC-7789 was on October 2, 1997 at
the Okie-Tex star party at Lake Murray, Oklahoma. At an
altitude of 872 feet, it was warm, dry (37% humidity according
to Jason Ware) and a slight breeze. Using my home-built 16inch f/6.4, at 81X, it filled 3/4 of the field. The object was a dim
peppering of even magnitude stars. Most appeared to be blue.
My second observation was on September 18, 2009 from
Cathedral Gorge State Park in East-Central Nevada. At an
altitude of 4,800 feet, it was calm, warm, but lots of clouds. It
was supposed to be clearing by 10 or so. It actually did, and I got some good viewing until just before midnight
when some more clouds came in. Using my commercial 16-inch f/6.4 at a magnification of 70X, a German
acquaintance said this object was his favorite open cluster. However, it was so dim, I wondered why he thought
it was so great. A moment later, I remembered that I’d forgot to take the O-III filter off after looking at IC0063! Once I removed the filter, wow! It looked great. Quite impressive and a very dense open cluster,
especially within the rich star field.
I observed it again on September 25, 2009 from Redstone Picnic Area on the North Shore Road at Lake Mead,
Nevada. At an altitude of 2,100 feet, the breeze stayed calm and it was warm all night. However, there was
some high-altitude junk that moved in and made the sky glow. The 1/4 moon made it worse and I had a real
hard time finding anything. Using my 16-inch f/6.4 at 70X, the cluster was a nice, rich sprinkling of stars. Not
as bright as it was at Cathedral Gorge.
For this challenge, I obtained my most recent observation, once again at Cathedral Gorge State Park on
September 11, 2015. A bit clearer than the night before and the transparency was much better. No puffy clouds
either. The mush was much lower to the horizon and the view was superb. However, seeing was bad and
Saturn looked terrible. However, that wasn’t my concern. The air stayed calm except an occasional zephyr.
The temp never dropped as bad as the night before. An outstanding night. Using my 16-inch f/4.5 at 102X, I
got the best view of the cluster yet and the one
I based my drawing on. It was a nice
peppering of maybe 70-80 bluish stars of
mostly even mag. There were probably well
more stars but I didn’t try to count that many.
It was almost 3-D. I saw one bright yelloworange star on outer edge while the rest were
bluish-white. I never saw the rose patterns
others have seen with smaller scopes because
my aperture resolved way too many stars. At
times, with the slight background haze, I
almost had the impression of a partially
resolved globular with the rest hidden in the
background. The drawing only shows the core
concentration because the spread of dimmer
stars goes out further but much looser and I
couldn’t accurately draw them. Besides, I
wasn’t sure they were even part of the cluster.
Jaakko Saloranta: LVAS Friend from Finland
Despite poor observing conditions, I
saw a rich and very beautiful cluster.
The strong background glow was lost
at high magnification. Several dark
pathways were visible within the
cluster as starless regions. Brighter
stars were concentrated toward the W
edge. ~80 stars within 9' down to
mag. 13. It resembles an open rose.
Sketch done @ 101X (30') using a
4.5-inch reflector.
Jay And Liz Thompson: LVAS Members from
Henderson, Nevada
We viewed NGC-7789 from several locations with a 17inch Newtonian telescope and a 14-inch SCT.
From the dark skies of Meadview, Arizona, NGC-7789 in
Cassiopeia is a big and bright open cluster. In the 3-inch
f/4 at 18X, it showed well. With the 17-inch at 63X it
was nice, and at 125X, it was truly awesome.
With the 17-inch under great skies at Cathedral Gorge, it
took up a considerable fraction of the view at 95X when
using an eyepiece with a 100° apparent field of view. It was very rich and reasonably compressed. It was a
definite addition to our favorites list.
From the Redstone picnic area of the LMRA using
the 17-inch, at 95X, we noted several red giant
stars showing a definite orange tint. At 227X, the
cluster took up the whole field of view, though the
tints of the red giants were not as pronounced.
We also observed it with a 14-inch SCT from our
moderately light-polluted back yard at the edge of
Henderson, NV. On first glance at 98X, the cluster
appeared rather sparse and loose, quite unlike the
view with the 17-inch from a dark sky location. As
we continued to observe, dimmer members became
visible and filled in the areas between the brighter
members. Though not as impressive as when
viewed under ideal conditions, the cluster still
provided a pleasing view. It was well framed in
the field of view at 98X, and filled the field of view
at 279X.
We also viewed Espin 38 with the 14-inch SCT. Espin 38 appeared at the edge of NGC-7789, and was a double
star that had a carbon star (Wildt’s Red Star, V532 Cas) as the dimmer companion. Espin 38 was discussed by
Sue French in the December, 2014 issue of Sky and Telescope.
AAVSO Ephemeris for maxima of V532 Cas are:
2456538.000 02 Sep 2013 12:00
2456988.000 26 Nov 2014 12:00
2457438.000 19 Feb 2016 12:00
We viewed Espin 38 on November 18, 2015,
three months prior to the closest maximum of the
carbon star. We’ll revisit Espin 38 closer to
maximum. At 98X, we saw the mag. 9.7 primary
as white, with a dim companion. Upon closer
scrutiny (and obtaining a precise focus), the
companion had a definite garnet gleam. The
color was easier to see at 98X than at 279X.
We also imaged the central part of NGC-7789 and
Espin 38 with the 14-inch SCT. Images are
attached.